In general, the process of mounting electronic components on a printed circuit board proceeds in the order of: applying solder onto the pad of a printed circuit board through screen printer equipment; inspecting the solder application state through solder paste inspection (SPI) equipment; and mounting the electronic components through component mounting equipment by using a surface mount technology (SMT).
Here, the screen printer applies the solder onto a pad of the printed circuit board by applying a solder paste in a state that a stencil mask having an opening is arranged on the printed circuit board, wherein the opening is formed in an area corresponding to a position of the pad formed on the printed circuit board.
When printing the solder paste through the screen printer as described above, there is a problem in which an error occurs in the position of the solder that is actually printed because of an alignment error of the stencil mask, a mismatch between the fiducial mark camera coordinate system inside the screen printer and the printed circuit board or the mask correction coordinate system, or the like.
In addition, there is another problem in which the amount of solder printed on the pad position of the printed circuit board is less or more than a reference value, or the like, due to a defect of the stencil mask.
Thus, in order to solve the problems, the screen printer and the solder inspection apparatus are configured to communicate with each other, and the solder inspection apparatus can generate feedback information and transmit the feedback information to the screen printer, wherein the feedback information includes a correction value for correcting the position of solder when the screen printer prints the solder, a check signal for checking the stencil mask of the screen printer, or the like.
However, in a case where a buffer configured to put the printed circuit board to be introduced into the solder inspection apparatus on standby is disposed between the screen printer and the solder inspection apparatus, and the feedback information is generated without considering the buffer, an excessive correction may occur in the screen printer or a check signal requesting the checking of the screen printer may occur too frequently.
Therefore, in the case where one or more buffers are disposed between the screen printer and the solder inspection apparatus and configured to put the printed circuit boards on standby, a method is required to improve the reliability of the feedback information that is generated by the solder inspection apparatus in consideration of the buffers.